The present invention relates to water-in-oil emulsions, particularly to water-in-oil emulsions of acrylate polymers wherein the polymer is stabilized with a water-soluble thiosulfate, thiocyanate, thiourea or nitrite.
Many water-soluble polymers, particularly water-soluble polyacrylates, are known to be effective thickeners and flocculating agents in aqueous solutions. Accordingly, the water-soluble polyacrylates are useful in the clarification of aqueous systems, in paper making operations, in the treatment of sewage and industrial waste and as stabilizers for drilling muds and enhanced oil drilling operations.
Heretofore, such polymers have generally been made available commercially as powders or finely divided solids which must subsequently be dissolved in an aqueous medium to be used. Often, due to the slow rate of dissolution and the tendency of the polymer to clump or agglomerate, such dissolution is time consuming and requires rather expensive mixing equipment. For these reasons, it has become common practice to formulate the water-soluble acrylate polymers in a water-in-oil emulsion wherein the polymer is dissolved in a disperse aqueous phase. Such emulsions, as well as their method of preparation, are described in U.S. Pat. No. 3,284,393. Unfortunately, the acrylate polymers in the emulsion are sufficiently unstable that, upon standing, they degrade and exhibit reduced activity. For this reason, water-in-oil emulsions of acrylate polymers can only be stored for a limited period of time prior to use.
In view of the limited stability of an acrylate polymer in water-in-oil emulsions thereof, it would be highly desirable to provide a water-in-oil emulsion of a water-soluble acrylate polymer having improved stability.